CoreStore/HardcoreData/NSManagedObjectContext+HardcoreData.swift

//
//  NSManagedObjectContext+HardcoreData.swift
//  HardcoreData
//
//  Copyright (c) 2014 John Rommel Estropia
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in all
//  copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//  SOFTWARE.
//

import Foundation
import CoreData
import GCDKit

private var _HardcoreData_NSManagedObjectContext_shouldCascadeSavesToParent: Void?

public extension NSManagedObjectContext {
    
    // MARK: - Public
    
    // MARK: Transactions
    
    public func temporaryContext() -> NSManagedObjectContext {
        
        let context = NSManagedObjectContext(concurrencyType: .PrivateQueueConcurrencyType)
        context.parentContext = self
        context.setupForHardcoreDataWithContextName("com.hardcoredata.temporarycontext")
        context.shouldCascadeSavesToParent = true
        
        return context
    }
    
    
    // MARK: Querying
    
    public func findFirst<T: NSManagedObject>(entity: T.Type) -> T? {
        
        return self.findFirst(T.self, predicate: NSPredicate(value: true))
    }
    
    public func findFirst<T: NSManagedObject>(entity: T.Type, predicate: NSPredicate) -> T? {
        
        let fetchRequest = NSFetchRequest()
        fetchRequest.entity = NSEntityDescription.entityForName(
            entity.entityName,
            inManagedObjectContext: self)
        fetchRequest.fetchLimit = 1
        
        var fetchResults: [T]?
        self.performBlockAndWait {
            
            var error: NSError?
            fetchResults = self.executeFetchRequest(fetchRequest, error: &error) as? [T]
            if fetchResults == nil {
                
                HardcoreData.handleError(
                    error!,
                    message: "Failed executing fetch request.")
            }
        }
        
        return fetchResults?.first
    }

    public func findAll<T: NSManagedObject>(entity: T.Type) -> [T]? {
        
        return self.findAll(QueryDescriptor<T>(entity: entity))
    }
    
    public func findAll<T: NSManagedObject>(query: QueryDescriptor<T>) -> [T]? {
        
        let fetchRequest = NSFetchRequest()
        fetchRequest.entity = NSEntityDescription.entityForName(
            query.entityName,
            inManagedObjectContext: self)
        
        var fetchResults: [T]?
        self.performBlockAndWait {
            
            var error: NSError?
            fetchResults = self.executeFetchRequest(fetchRequest, error: &error) as? [T]
            if fetchResults == nil {
                
                HardcoreData.handleError(
                    error!,
                    message: "Failed executing fetch request.")
            }
        }
        
        return fetchResults
    }
    
    
    // MARK: - Internal
    
    internal func saveSynchronously() -> SaveResult {
        
        var result: SaveResult = SaveResult(hasChanges: false)
        if !self.hasChanges {
            
            self.reset()
            return result
        }
        
        self.performBlockAndWait {
            [unowned self] () -> () in
            
            var saveError: NSError?
            if self.save(&saveError) {
                
                if self.shouldCascadeSavesToParent {
                    
                    if let parentContext = self.parentContext {
                        
                        switch parentContext.saveSynchronously() {
                            
                        case .Success(let hasChanges):
                            result = SaveResult(hasChanges: true)
                        case .Failure(let error):
                            result = SaveResult(error)
                        }
                        return
                    }
                }
                
                result = SaveResult(hasChanges: true)
            }
            else if let error = saveError {
                
                HardcoreData.handleError(
                    error,
                    message: "Failed to save NSManagedObjectContext.")
                result = SaveResult(error)
            }
            else {
                
                result = SaveResult(hasChanges: false)
            }
        }
        
        return result
    }
    
    internal func saveAsynchronouslyWithCompletion(completion: ((result: SaveResult) -> ())?) {
        
        if !self.hasChanges {
            
            self.reset()
            if let completion = completion {
                
                GCDBlock.async(.Main) {
                    
                    completion(result: SaveResult(hasChanges: false))
                }
            }
            return
        }
        
        self.performBlock {
            [unowned self] () -> () in
            
            var saveError: NSError?
            if self.save(&saveError) {
                
                if self.shouldCascadeSavesToParent {
                    
                    if let parentContext = self.parentContext {
                        
                        parentContext.saveAsynchronouslyWithCompletion(completion)
                        return
                    }
                }
                
                if let completion = completion {
                    
                    GCDBlock.async(.Main) {
                        
                        completion(result: SaveResult(hasChanges: true))
                    }
                }
            }
            else if let error = saveError {
                
                HardcoreData.handleError(
                    error,
                    message: "Failed to save NSManagedObjectContext.")
                if let completion = completion {
                    
                    GCDBlock.async(.Main) {
                        
                        completion(result: SaveResult(error))
                    }
                }
            }
            else if let completion = completion {
                
                GCDBlock.async(.Main) {
                    
                    completion(result: SaveResult(hasChanges: false))
                }
            }
        }
    }
    
    internal class func rootSavingContextForCoordinator(coordinator: NSPersistentStoreCoordinator) -> NSManagedObjectContext {
        
        let context = NSManagedObjectContext(concurrencyType: .PrivateQueueConcurrencyType)
        context.persistentStoreCoordinator = coordinator
        context.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
        context.setupForHardcoreDataWithContextName("com.hardcoredata.rootcontext")
        
        return context
    }
    
    internal class func mainContextForRootContext(rootContext: NSManagedObjectContext) -> NSManagedObjectContext {
        
        let context = NSManagedObjectContext(concurrencyType: .MainQueueConcurrencyType)
        context.parentContext = rootContext
        context.setupForHardcoreDataWithContextName("com.hardcoredata.maincontext")
        context.shouldCascadeSavesToParent = true
        context.registerForNotificationsWithName(
            NSManagedObjectContextDidSaveNotification,
            fromObject: rootContext,
            targetQueue: NSOperationQueue.mainQueue()) {
            [unowned context] (note) -> () in
                
            context.mergeChangesFromContextDidSaveNotification(note)
        }
        
        return context
    }
    
    
    // MARK: - Private
    
    private var shouldCascadeSavesToParent: Bool {
        
        get {
            
            if let value = objc_getAssociatedObject(self, &_HardcoreData_NSManagedObjectContext_shouldCascadeSavesToParent) as? NSNumber {
                
                return value.boolValue
            }
            return false
        }
        set {
            
            objc_setAssociatedObject(
                self,
                &_HardcoreData_NSManagedObjectContext_shouldCascadeSavesToParent,
                newValue,
                objc_AssociationPolicy(OBJC_ASSOCIATION_ASSIGN))
        }
    }
    
    private func setupForHardcoreDataWithContextName(contextName: String) {
        
        if self.respondsToSelector("setName:") {
            
            self.name = contextName
        }
        
        self.registerForNotificationsWithName(NSManagedObjectContextWillSaveNotification, fromObject: self) {
            (note) -> () in
            
            let context: NSManagedObjectContext = note.object as NSManagedObjectContext
            let insertedObjects = context.insertedObjects
            if insertedObjects.count <= 0 {
                
                return
            }
            
            var permanentIDError: NSError?
            if context.obtainPermanentIDsForObjects(insertedObjects.allObjects, error: &permanentIDError) {
                
                return
            }
            
            if let error = permanentIDError {
                
                HardcoreData.handleError(
                    error,
                    message: "Failed to obtain permanent IDs for inserted objects.")
            }
        }
    }
}